Welcome to the promise of the Internet at 33,000 feet — and the questions of etiquette, openness and free speech that airlines and service providers will have to grapple with as they bring Internet access to the skies in the coming months.

"This gets into a ticklish area," said Vint Cerf, one of the Internet's chief inventors and generally a critic of network restrictions. "Airlines have to be sensitive to the fact that customers are (seated) close together and may be able to see each other's PC screens. More to the point, young people are often aboard the plane."

Technology providers and airlines are already making decisions. Some will block services like Internet phone calls altogether while others will put limits and install filters on content. And traffic management tools that are frowned upon on terra firma could be commonplace in the air.

He said airlines based in more restrictive countries could choose to expand the list.

The company also is recommending that airlines permit Internet-based phone calls only on handsets with wireless Wi-Fi capabilities — the technology delivering access within the passenger cabin. Bruner said the company believes Wi-Fi handsets use less bandwidth than telephone software that runs on laptops.

Airlines, he said, also could block incoming calls — and the annoying ring tones they produce — or designate periods of quiet time.

OnAir, which has European certification for airborne cellular services, plans to give airlines similar choices, Chief Executive Benoit Debains said. Although some airlines are concerned about noise, Debains said, enabling voice would generate more revenue than data-only services.

Air France, which plans to start allowing cellular calls through OnAir within months, said it would see how people use such services before crafting rules.

"Are you going to reach your wife to tell her what you did the entire day or just tell her, `Can you pick me up at the airport?'" Air France spokeswoman Marina Tymen said, adding that passengers might tell the airline that data services fulfill all their needs.

U.S. airlines are largely taking the opposite approach.

With possible exceptions for crew and federal air marshals, flights on AMR Corp.'s American Airlines and Alaska Air Group Inc.'s Alaska Airlines won't have access to Internet-based phone services like eBay Inc.'s Skype.

Discount startup Virgin America is also considering a ban.

"An airborne environment is a confined environment," said Charles Ogilvie, Virgin's director of in-flight entertainment and partnerships. "You don't want 22B yapping away or playing on a boom box."

Airlines have offered in-flight phone services before, but their high costs have limited their popularity. By contrast, Internet phone calls are free or cheap, particularly for passengers already paying for in-flight access to check e-mail or surf Web sites.

Meanwhile, American, Alaska and Virgin have no plans to filter sites based on their content. At most, an airline may manage traffic and delay large downloads, or in Virgin's case give passengers the option of enabling controls for their kids.

"We think decency and good sense and normal behavior" will prevail, said Jack Blumenstein, chief executive of Aircell LLC, which is launching service on some American and Virgin flights in 2008.

Alaska, which plans to start offering service on some flights in the spring, said the same guidelines apply whether a passenger is flipping through a magazine, watching a DVD on a laptop or surfing the Web.

"Occasionally we do have conversations with customers about content," Alaska spokeswoman Amanda Tobin Bielawski said.

In many ways, airlines are facing issues similar to those encountered by Wi-Fi networks on the ground — at airports, coffee shops and other public places.

Glenn Fleishman, editor of the Wi-Fi Networking News site, said operators of public networks generally do not filter because users are conscious that others can see what they surf. A coffee shop employee might occasionally ask a customer to leave, Fleishman said, "but those stories tend to be pretty far between."

Airplanes, however, are different because customers are in closer quarters and are more likely to include kids.

Allowing porn could subject an airline to harassment complaints much like an employer that refuses to clamp down, said John Palfrey, a Harvard Law School professor.

"I think they have a right to (filter), but I come up short of saying they have the responsibility," Palfrey said. "I'd rather have the responsibility in the hands of passengers and require them to be accountable for what they do on laptops and airplanes."

Airborne Internet activities — such as hacking and piracy — could raise new questions about which country's laws apply.

The in-flight services also could exacerbate long-standing grievances.

What if the passenger in front of you wants to recline, making it difficult to surf comfortably on your laptop? What if you're finishing a crucial e-mail on deadline and an adjacent passenger needs to leave for the bathroom? What if the person next to you keeps peering over while you're trying to review a confidential Web site?

Steve Jones, a University of Illinois at Chicago professor who specializes in Internet studies, said passengers and flight crews would need to undergo "the kinds of learning the ropes and learning the etiquette anytime we put new technology in new settings."

Just as most people have come to set boundaries for cell phone use in public settings, he said, "we will see develop social norms for using the Internet in flight."